5.1 Al(001) slab: separate thickness from vacuum

These are unexecuted teaching inputs and starting models. Original diagrams are schematics, not calculated results. Validate version-specific syntax, licensed or authorized data, numerical convergence and the scientific model before using this workflow.

5.1.1 Model, units and provenance

PW cutoffs and energies use Ry, common force output uses Ry/bohr, and pressure uses kbar. Geometry cards state their coordinate units. Different executables have distinct grammars and time-unit conventions.

Shared inputs, conventions and evidence

Original schematic: Al(001) slab: separate thickness from vacuum. No numerical results are claimed.

5.1.2 Unexecuted inputs and explicit deltas

Use the accompanying instructions to identify the parent calculation and placement of every delta; a snippet is not automatically a standalone input. Preserve all blank-line and file-provenance requirements.

5.1.2.1 Input block 1

! Delta from Al-base: ibrav=0, nat=10; remove A.
! calculation='relax'; fixed cell, metallic occupations retained.
CELL_PARAMETERS angstrom
4.05 0.00 0.00
0.00 4.05 0.00
0.00 0.00 24.00
ATOMIC_POSITIONS angstrom
Al 0.000 0.000 7.950
Al 2.025 2.025 7.950
Al 0.000 2.025 9.975
Al 2.025 0.000 9.975
Al 0.000 0.000 12.000 0 0 0
Al 2.025 2.025 12.000 0 0 0
Al 0.000 2.025 14.025
Al 2.025 0.000 14.025
Al 0.000 0.000 16.050
Al 2.025 2.025 16.050
K_POINTS automatic
10 10 1 0 0 0

5.1.3 Worked investigation

5.1.3.1 Intuition and prerequisites

A slab has two independent finite-size errors: interaction between its two surfaces through the material, and interaction between repeated slabs through vacuum. Increasing only vacuum cannot fix a slab that is too thin. Begin with Al-base at a converged bulk lattice, then construct a symmetric clean (001) slab. The example below uses the unrelaxed teaching value a=4.05 Å; replace it consistently with your bulk result.

5.1.3.2 Original five-layer geometry

See input block 1 above.

5.1.3.3 Outputs, checks and exercise

For equivalent clean surfaces, γ=(E_slab−N E_bulk/atom)/(2A). Match functional, pseudopotentials, cutoffs and metallic integration carefully; cancellation can be poor if the bulk reference has a different numerical bias. Report interlayer relaxations as well as γ, and distinguish slab height from the actual empty gap. Exercise: repeat with only the bottom layers fixed and explain why asymmetric constraints can change relaxation and electrostatics even for the same atom count.